Australia's Sally Pearson, third top, heads to the line to win the gold medal in the final of the Women's 100m hurdles during the World Athletics Championships in London Saturday, Aug. 12, 2017. (AP Photo/David J. Phillip)

Australia's Sally Pearson, right, crosses the finish line to win the Women's 100 meters hurdles final at the World Athletics Championships in London Saturday, Aug. 12, 2017. (AP Photo/Martin Meissner)

Sally Pearson celebrates on the podium at the World Athletics Championships in London Saturday, Aug. 12, 2017. (AP Photo/Martin Meissner)

Sally Pearson, right, in action on her way to winning the gold medal in the women's 100-meter hurdles final during the World Athletics Championships in London Saturday, Aug. 12, 2017.. (AP Photo/Frank Augstein)

Australia's Sally Pearson, left, crosses the line to win gold in the women's 100-meter hurdles final during the World Athletics Championships in London Saturday, Aug. 12, 2017. (AP Photo/Matthias Schrader)

Sally Pearson is world champion again. After three lost years ruined by injury, Pearson has completed the most remarkable comeback to win gold at the London world championships and in doing so has been elevated among the greatest Australian athletes ever.

Pearson now stands alongside Catherine Freeman as one of Australia's best modern track athletes after adding a second world championship gold to a silver in Moscow and her Olympic gold and silver.

This victory, she admits, is as sweet as any after the journey she has undertaken to get here - four years lost from major championships, putting aside the lesser Commonwealth Games, ruined by serious calf, Achilles and hamstring injuries as well as a wrist shattered in a fall.

On top of that she sacked her last coach and began coaching herself on the day the athletics began at the Rio Olympics last year and sat down in her Gold Coast home to write out a plan to get her back to the top of the world. Then on the eve of her 31st birthday she arrived in London as a relative outsider and won gold.

"Every single emotion that you can hold in your body just came out when I crossed that finish line. It wasn't surprise, it wasn't shock. I was just proud, so proud of what I had done to get here," she said after winning the gold in 12.59s.

"From the first day I started training I knew it was possible, I knew I could get here and I remember someone saying `you can be the world champion again' and I didn't feel awkward about that. When I knew I felt that, I knew it was in me to do it."

Her outsider, or challenger, status here made it feel a little sweeter than when she won her first world championship in Daegu six years ago.

"I think so, I went to Daegu and I was winning, right from a year out I was going to win the world championships," she said

"Every medal is different and this one sure is very different to the rest of them."

Pearson's success preceded a heartbreaking end to the career of Jamaican sprinter Usain Bolt, the Olympic champion appearing to strain a hamstring in the final leg of the men's 4x100m relay. He failed to finish and Great Britain won gold.

After taking the baton from his teammate Yohan Blake, Bolt began to gather speed only to pull up and shout in pain about 60m from the finish line.

It was hardly the farewell party that Bolt, the greatest sprinter in history, had in mind when he decided to make this meet the last of his career.

His injury - later confirmed as severe cramp - would normally have cast a pall over the rest of the race, but it has been a frustrating meet for Britain, the host country. And with Bolt on the ground and the Jamaicans out of contention, the gold came down to a sprint for the finish between Christian Coleman of the United States and Nethaneel Mitchell-Blake of Britain.

Britain won by 0.05 seconds, finishing in 37.47 seconds to the Americans' 37.52. As the official results flashed on the big screen, the crowd cheered wildly for Britain's second gold medal of these championships.

Meanwhile, Bolt's teammates rushed to help him as he lay on the track.